1. Field of the invention
The invention concerns a high-voltage circuit-breaker with an interrupting chamber comprising a gas-tight casing filled with a gas having good insulative properties such as sulfur hexafluoride and containing a fixed permanent contact, a fixed arc contact and a mobile assembly comprising permanent contacts and arc contacts, the chamber further comprising a shunt resistor connected by an auxiliary switch when the arc contacts are opened.
2. Description of the prior art
In single-interrupter type very high voltage circuit-breakers the conditions for interrupting line fault currents are very severe.
It is known to insert a breaking resistor R to improve line fault current interrupting. The presence of a resistor whose resistance value is approximately equal to the line impedance Z strongly reduces the rate of increase of the transient voltage and the amplitude of the first peak of oscillation of the line voltage. The reduction coefficient is equal to R/(R+Z) and Z=450 ohms for an overhead line. These interrupting resistors cannot be kept live for long because they absorb a large amount of energy. It is therefore necessary to associate with them a switch which must have a high rupture capacity to interrupt the residual current, especially under phase opposition conditions.
For currents exceeding several hundred amperes a gas-blast type switch is required, the relaxation time the time for which the current is regarded as negligible, being less than 1 ampere, for example is very short. This leads to the installation of complex pressurized gas auxiliary switches.
It is also known to use series varistors inserted during the interrupting operation.
A capacitor in parallel with these varistors improves the interruption of high line fault currents. For capacitors having a capacitance exceeding 5,000 pF this arrangement, although effective, is costly. The capacitor must be rated to withstand the phase opposition voltage for approximately one period of the voltage. Although this time is short, the capacitor is large. An arrangement of this kind is described in French patent application Fr 91 04173.
French patent application Fr 91 04173 describes very simple auxiliary switches requiring no gas blast for varistor-assisted interruption.
The present invention makes it possible to interrupt high resistive currents with auxiliary switches of this kind with no insulative gas blast.